1. Field of the Invention
This invention relates to a yarn feeding apparatus for knitting machines, particularly for circular knitting machines.
2. Description of the Prior Art
As well known, in multi-fall knitting machines, that is to say in those machines wherein a knitted fabric is formed through needles drawing a plurality of feeding yarns from a plurality of cops or the like, such yarns are drawn from the cops and fed to the needles through feeding apparatuses, each comprising a roller or wheel freely rotable about its own axis and having a substantially cylindrical shaped surface, on which yarn can be pressed and held by a belt of lower height than that of the roller or wheel advanced by means of a drive member.
The belt advancement causes the roller or wheel to rotate and draws the yarn from the relative actuation cop, which yarn, when released from the belt and roller or wheel, is thus supplied to the respective needle at predetermined speed.
In case of circular knitting machines, rollers or wheels of this type are arranged according to a circle at the machine top and the belt rotably driving the same is single and loop closed.
The need often occurs to move the filaments of yarn out of the contact with the belt, displacing the involved yarn in the direction of the roller or wheel axis laterally of said belt. The yarn slips on the surface of the roller or wheel, which continues to be rotably driven by the belt, but with the latter no longer acting on the yarn. This occurs, for example, when the stitch length has to be changed on the knitting machine, or when the type of fabric being produced by the machine has to be changed, or again when a knitted fabric is produced having stripes of different colors and when desiring to leave out the filaments of yarn of a given colors from the fabric being formed.
Since knitting machines operate at high speed, when the necessity occurs of discontinuing the supply of a given yarn, steps must be taken for high speed removal of the involved yarn from the position at which such a yarn is pressed between the belt and relevant roller or wheel.
Each of the yarn feeding apparatuses are provided with a movable outlet arm for the passage thereon of the yarn moving out of the apparatus, and which is responsive to the outlet yarn tension. Loosening of the outlet yarn tension decreases the pressure on said arm, which mechanically or otherwise acts upon a yarn insertion arm or a guiding slit, which is lifted and moves the yarn away out the pressure zone of the belt on the roller or wheel. The movable outlet arm is somewhat longer than the yarn insertion arm, and the yarn passing over the involved roller or wheel passes on two eyes, one integral with each of the two arms. As the yarn is withdrawn, both of the arms are displaced to the belt, so as to hold the yarn under the belt at a position substantially longitudinally of the belt. When the supply of the involved yarn has to be discontinued, displacement of the two arms draws the yarn out of the contact with the belt and relevant roller or wheel.
Feeding apparatuses of this type are well known and described, for example in the German Pat. No. 1,585,298 corresponding to U.S. Pat. No. 3,264,845 and in the published German Pat. application No. DOS 1,635,893, but have the disadvantage of requiring a relatively extended period of time between the time at which the movable outlet arm acts upon the movable inlet arm shifting the yarn laterally of the belt: such a time is determined by the required time that, following the side displacement of the inlet arm relative to the belt, the whole length of yarn, which is pressed between the belt and roller or wheel in parallel relationship to the belt, is withdrawn away from below the belt. In other words, for withdrawing the yarn away from the zone of contact between the belt and roller or wheel, the latter should rotate through an angle equal to the maximum angle according to which the contact between the belt and roller or wheel would occur.
Additionally, during the yarn feed the outlet arm takes a position that is determined by an outlet eye integral with such arm and by a location where the yarn leaves that zone at which it is pressed between the belt and roller or wheel. As a result, when the outlet arm is moved or driven to control arresting of the yarn feed, it is pulled towards the belt by the yarn which is substantially at an intermediate position to the belt. This implies that the movement of the outlet arm is considerably hindered.
Along with the above mentioned factor, this factor means that a relatively extended time is required between the time at which the arrest signal for the supply of a yarn is given and the time at which such a supply effectively ceases, which makes the apparatus unusable when the yarn insertion and/or disconnection has to be rapidly carried out.